1. The Field of the Invention
The present invention relates to assay methods to predict compound toxicity.
2. The Relevant Technology
A major reason for drugs to be withdrawn from the market after the drugs have been launched is because they may cause liver injury. The trend in drug discovery is efficient compound attrition where a compound's toxicity is identified as early as possible in the drug discovery process and thus the compound can be removed from further development. Due to regulatory, ethical and cost issues, the use of animal testing to identify potential hepatotoxic compounds early in the drug discovery process is often not feasible. The challenge is to identify an affordable in vitro assay method that can be used early in the drug discovery process and that can predict whether a compound is hepatotoxic with high specificity and sensitivity. Although there exists various methods to detect the potential hepatotoxicity of a drug compound, most perform poorly in predicting hepatotoxicity of the compound of interest.
Good predictivity for toxicity requires an assay which determines whether a compound is toxic with high specificity (i.e., a low percentage of false positives) and high sensitivity (i.e., a low percentage of false negatives). Previously, O'Brien et al. (Arch. Toxicol., 2006, 80:580-604) showed that the simultaneous measurement of multiple cell health indicators in hepatic cells using an automated quantitative imaging-based detection method (i.e., high content imaging) predicted drug hepatotoxicity with high sensitivity and specificity. A more recent study by Xu et al. (Toxicological Sciences, 2008, 105(1):97-105) using a similar high-content imaging approach but directed towards different cellular targets also showed that a high-content, quantitative, cell-imaging based assay on hepatic cells can predict the hepatotoxicity of compounds. Although the above-cited methods have been used to predict the potential hepatotoxicity of compounds with good sensitivity and specificity, the lack of convenience, robustness and ease of use of these assay methods have hindered their adoption as assays to be routinely performed for compound hepatotoxicity detection.
A challenge in determining compound toxicity is that different cellular targets exhibit toxic responses at different doses for different compounds. For example, in a condition called hormesis, a compound may show its toxicity at an intermediate concentration but not at a higher concentration. Previous work in the art has not dealt with this issue, as conventional methods either monitor toxicity at a specific compound dose (e.g., Xu et al.) or use a compound's EC50/IC50 concentration to assess toxicity (e.g., O'Brien et al.). However, many cellular targets do not exhibit a classic sigmoidal dose-response curve with many compounds and may also exhibit hormesis-like effects, making it difficult to determine the EC50/IC50 concentration of the compounds for a specific target. A method to robustly deal with the variations in specific target response and to accurately assess compound toxicity by monitoring a range of concentrations would improve the predictivity of toxicity assays.